For years, proponents of the hydrogen economy have argued that hydrogen will replace traditional hydrocarbon fuels for transportation purposes. But, so far, a lack of new, inexpensive methods for hydrogen production and storage has impeded this goal. Over the last several years, an MIT professor has been pushing cobalt catalysts as a cheap replacement for the expensive metals typically used to split water. A paper in this week's Proceedings of the National Academies of Science describes the latest progress here: integrating the cobalt catalyst with a silicon solar cell to create a device that uses the sun to split water.

Hydrogen is a desirable fuel, because when it is burned or otherwise consumed (as in a fuel cell), it only produces water, although combustion results in small amounts of nitrogen oxides as by-products. However, unlike traditional liquid or gas fuels, hydrogen doesn't exist in its molecular form on Earth, so it must be produced from other sources—it is an energy carrier, rather than an energy source.